add 3x3p1_scalar kernel

PiperOrigin-RevId: 274778298
diff --git a/BUILD b/BUILD
index ccd45c0..ee85055 100644
--- a/BUILD
+++ b/BUILD
@@ -85,6 +85,7 @@
     "src/f32-dwconv/up1x25-scalar.c",
     "src/f32-dwconv/up1x4-scalar.c",
     "src/f32-dwconv/up1x9-scalar.c",
+    "src/f32-dwconv-spchw/3x3p1-scalar.c",
     "src/f32-gavgpool/mp7p7q-scalar.c",
     "src/f32-gavgpool/up7-scalar.c",
     "src/f32-gemm/1x4-scalar.c",